Power cables insulated with extruded dielectrics are known to suffer from shortened life when installed underground where water contact is likely. The shortened life has been attributed to the formation of water trees, which occur when an organic polymeric material is subjected to an electrical field over a long period of time in the presence of water in liquid or vapor form. The net result is a reduction in the dielectric strength of the insulation.
Many solutions have been proposed for increasing the resistance of organic insulating materials to degradation by water treeing. These include, for example, the addition to polyethylene of (i) a polar copolymer such as a copolymer of ethylene and vinyl acetate; (ii) a voltage stabilizer such as dodecanol; and (iii) a filler, e.g., clay. These solutions all have shortcomings of some kind such as an increase in dielectric loss, i.e., the power factor, volatility, or cost.